I’d love to go through this with you step by step but there is a fantastic guide and no reason to duplicate the work. You can find it here. This will set your Raspberry Pi up and configure it as a wifi hotspot. If you can carefully follow directions and cut and paste commands into a terminal you can do this. You can.

Once you get it Rasbian configured as a hotspot plug in the 3g dongle and open a terminal and type:

Just to make sure I can do this on the road I made sure it worked in Japan first. Had to plunk down $40 for a 1Gig Data Card for Japan to test. Got the card from here And by the way if you travel to Japan this may be the cheapest SIM card to get with the best coverage. If you have an unlocked phone or modem give it a try. Works for 14 days.